Calcium is a major nutritional requirement of human embryonic development, needed particularly in skeletal formation and the maintenance of neuromuscular functions and blood coagulation mechanisms. The organ responsible for mobilizing extraembryonic calcium into the fetal circulation is the placenta. Previous studies by this investigator have shown that the animal placenta experimental model, the chorioallantoic membrane (CAM) of the chick embryo, contains a specific calcium-binding protein which appears to be involved in the transport of eggshell calcium by the CAM. Recent preliminary investigations reveal that human placental tissues also contain a specific high-molecular-weight calcium-binding protein (HCaBP). I propose to study the HCaBP as a potential functional marker molecule of the transplacental calcium transport process. The HCaBP will be isolated and purified, using a 4-step procedure. Its composition, physiochemical properties, and activity will be determined and characterized. Specific anti-HCaBP antibodies will be prepared in rabbits and used for fluorescent and ultrastructural immunohistochemical localization of the HCaBP in placental cells. The expression of HCaBP will be studied with respect to rate, turnover, and subcellular mode and site of synthesis. Finally, potential effector substances which regulate HCaBP expression will be identified. Results from these studies should indicate how the specific placental HCaBP may be involved in the mechanism of transplacental calcium transport and shed light on the regulation of calcium metabolism during fetal development. The information gathered here should also contribute to the understanding of prenatal nutrition in general and the underlying causes of birth defects, specifically those related to imbalance in calcium metabolism.